X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FRegisterScavenging.cpp;h=67bf209c73250ab44ef32f98d0682d95f9379304;hb=030c4bfbc9885444b8a5ad0b5f1e50045a351d17;hp=e595a36b598915668edbbf4c18f43a8c49f58040;hpb=e689ce626ce1d0022f70fb4a85113590bbdbb5e9;p=oota-llvm.git diff --git a/lib/CodeGen/RegisterScavenging.cpp b/lib/CodeGen/RegisterScavenging.cpp index e595a36b598..67bf209c732 100644 --- a/lib/CodeGen/RegisterScavenging.cpp +++ b/lib/CodeGen/RegisterScavenging.cpp @@ -100,54 +100,12 @@ void RegScavenger::enterBasicBlock(MachineBasicBlock *mbb) { CalleeSavedRegs.set(CSRegs[i]); } - // RS used within emit{Pro,Epi}logue() - if (mbb != MBB) { - MBB = mbb; - initRegState(); - } + MBB = mbb; + initRegState(); Tracking = false; } -#ifndef NDEBUG -/// isLiveInButUnusedBefore - Return true if register is livein the MBB not -/// not used before it reaches the MI that defines register. -static bool isLiveInButUnusedBefore(unsigned Reg, MachineInstr *MI, - MachineBasicBlock *MBB, - const TargetRegisterInfo *TRI, - MachineRegisterInfo* MRI) { - // First check if register is livein. - bool isLiveIn = false; - for (MachineBasicBlock::const_livein_iterator I = MBB->livein_begin(), - E = MBB->livein_end(); I != E; ++I) - if (Reg == *I || TRI->isSuperRegister(Reg, *I)) { - isLiveIn = true; - break; - } - if (!isLiveIn) - return false; - - // Is there any use of it before the specified MI? - SmallPtrSet UsesInMBB; - for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg), - UE = MRI->use_end(); UI != UE; ++UI) { - MachineOperand &UseMO = UI.getOperand(); - if (UseMO.isReg() && UseMO.isUndef()) - continue; - MachineInstr *UseMI = &*UI; - if (UseMI->getParent() == MBB) - UsesInMBB.insert(UseMI); - } - if (UsesInMBB.empty()) - return true; - - for (MachineBasicBlock::iterator I = MBB->begin(), E = MI; I != E; ++I) - if (UsesInMBB.count(&*I)) - return false; - return true; -} -#endif - void RegScavenger::addRegWithSubRegs(BitVector &BV, unsigned Reg) { BV.set(Reg); for (const unsigned *R = TRI->getSubRegisters(Reg); *R; R++) @@ -167,7 +125,7 @@ void RegScavenger::forward() { Tracking = true; } else { assert(MBBI != MBB->end() && "Already at the end of the basic block!"); - MBBI = next(MBBI); + MBBI = llvm::next(MBBI); } MachineInstr *MI = MBBI; @@ -216,14 +174,35 @@ void RegScavenger::forward() { if (!Reg || isReserved(Reg)) continue; if (MO.isUse()) { - assert(isUsed(Reg) && "Using an undefined register!"); + if (!isUsed(Reg)) { + // Check if it's partial live: e.g. + // D0 = insert_subreg D0, S0 + // ... D0 + // The problem is the insert_subreg could be eliminated. The use of + // D0 is using a partially undef value. This is not *incorrect* since + // S1 is can be freely clobbered. + // Ideally we would like a way to model this, but leaving the + // insert_subreg around causes both correctness and performance issues. + bool SubUsed = false; + for (const unsigned *SubRegs = TRI->getSubRegisters(Reg); + unsigned SubReg = *SubRegs; ++SubRegs) + if (isUsed(SubReg)) { + SubUsed = true; + break; + } + assert(SubUsed && "Using an undefined register!"); + } assert((!EarlyClobberRegs.test(Reg) || MI->isRegTiedToDefOperand(i)) && "Using an early clobbered register!"); } else { assert(MO.isDef()); +#if 0 + // FIXME: Enable this once we've figured out how to correctly transfer + // implicit kills during codegen passes like the coalescer. assert((KillRegs.test(Reg) || isUnused(Reg) || isLiveInButUnusedBefore(Reg, MI, MBB, TRI, MRI)) && "Re-defining a live register!"); +#endif } } @@ -248,81 +227,83 @@ static void CreateRegClassMask(const TargetRegisterClass *RC, BitVector &Mask) { Mask.set(*I); } -unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass, - const BitVector &Candidates) const { - // Mask off the registers which are not in the TargetRegisterClass. - BitVector RegsAvailableCopy(NumPhysRegs, false); - CreateRegClassMask(RegClass, RegsAvailableCopy); - RegsAvailableCopy &= RegsAvailable; - - // Restrict the search to candidates. - RegsAvailableCopy &= Candidates; - - // Returns the first unused (bit is set) register, or 0 is none is found. - int Reg = RegsAvailableCopy.find_first(); - return (Reg == -1) ? 0 : Reg; -} - -unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass, - bool ExCalleeSaved) const { - // Mask off the registers which are not in the TargetRegisterClass. - BitVector RegsAvailableCopy(NumPhysRegs, false); - CreateRegClassMask(RegClass, RegsAvailableCopy); - RegsAvailableCopy &= RegsAvailable; - - // If looking for a non-callee-saved register, mask off all the callee-saved - // registers. - if (ExCalleeSaved) - RegsAvailableCopy &= ~CalleeSavedRegs; - - // Returns the first unused (bit is set) register, or 0 is none is found. - int Reg = RegsAvailableCopy.find_first(); - return (Reg == -1) ? 0 : Reg; +unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RC) const { + for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); + I != E; ++I) + if (!isAliasUsed(*I)) + return *I; + return 0; } -/// DistanceMap - Keep track the distance of an MI from the current position. -typedef DenseMap DistanceMap; +/// findSurvivorReg - Return the candidate register that is unused for the +/// longest after MBBI. UseMI is set to the instruction where the search +/// stopped. +/// +/// No more than InstrLimit instructions are inspected. +/// +unsigned RegScavenger::findSurvivorReg(MachineBasicBlock::iterator StartMI, + BitVector &Candidates, + unsigned InstrLimit, + MachineBasicBlock::iterator &UseMI) { + int Survivor = Candidates.find_first(); + assert(Survivor > 0 && "No candidates for scavenging"); + + MachineBasicBlock::iterator ME = MBB->getFirstTerminator(); + assert(StartMI != ME && "MI already at terminator"); + MachineBasicBlock::iterator RestorePointMI = StartMI; + MachineBasicBlock::iterator MI = StartMI; + + bool inVirtLiveRange = false; + for (++MI; InstrLimit > 0 && MI != ME; ++MI, --InstrLimit) { + bool isVirtKillInsn = false; + bool isVirtDefInsn = false; + // Remove any candidates touched by instruction. + for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { + const MachineOperand &MO = MI->getOperand(i); + if (!MO.isReg() || MO.isUndef() || !MO.getReg()) + continue; + if (TargetRegisterInfo::isVirtualRegister(MO.getReg())) { + if (MO.isDef()) + isVirtDefInsn = true; + else if (MO.isKill()) + isVirtKillInsn = true; + continue; + } + Candidates.reset(MO.getReg()); + for (const unsigned *R = TRI->getAliasSet(MO.getReg()); *R; R++) + Candidates.reset(*R); + } + // If we're not in a virtual reg's live range, this is a valid + // restore point. + if (!inVirtLiveRange) RestorePointMI = MI; -/// Build a distance map for instructions from I to E. -static void buildDistanceMap(DistanceMap &DM, - MachineBasicBlock::iterator I, - MachineBasicBlock::iterator E) { - DM.clear(); - for (unsigned d = 0; I != E; ++I, ++d) - DM.insert(DistanceMap::value_type(I, d)); -} + // Update whether we're in the live range of a virtual register + if (isVirtKillInsn) inVirtLiveRange = false; + if (isVirtDefInsn) inVirtLiveRange = true; -/// findFirstUse - Calculate the distance to the first use of the -/// specified register in the range covered by DM. -static MachineInstr *findFirstUse(const MachineBasicBlock *MBB, - const DistanceMap &DM, - unsigned Reg, - unsigned &Dist) { - const MachineRegisterInfo *MRI = &MBB->getParent()->getRegInfo(); - MachineInstr *UseMI = 0; - Dist = ~0U; - for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(Reg), - RE = MRI->reg_end(); RI != RE; ++RI) { - MachineInstr *UDMI = &*RI; - if (UDMI->getParent() != MBB) + // Was our survivor untouched by this instruction? + if (Candidates.test(Survivor)) continue; - DistanceMap::const_iterator DI = DM.find(UDMI); - if (DI == DM.end()) - continue; - if (DI->second < Dist) { - Dist = DI->second; - UseMI = UDMI; - } + + // All candidates gone? + if (Candidates.none()) + break; + + Survivor = Candidates.find_first(); } - return UseMI; + // If we ran off the end, that's where we want to restore. + if (MI == ME) RestorePointMI = ME; + assert (RestorePointMI != StartMI && + "No available scavenger restore location!"); + + // We ran out of candidates, so stop the search. + UseMI = RestorePointMI; + return Survivor; } unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC, MachineBasicBlock::iterator I, int SPAdj) { - assert(ScavengingFrameIndex >= 0 && - "Cannot scavenge a register without an emergency spill slot!"); - // Mask off the registers which are not in the TargetRegisterClass. BitVector Candidates(NumPhysRegs, false); CreateRegClassMask(RC, Candidates); @@ -332,44 +313,20 @@ unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC, // Exclude all the registers being used by the instruction. for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { MachineOperand &MO = I->getOperand(i); - if (MO.isReg()) + if (MO.isReg() && MO.getReg() != 0 && + !TargetRegisterInfo::isVirtualRegister(MO.getReg())) Candidates.reset(MO.getReg()); } - // Prepare to call findFirstUse() a number of times. - DistanceMap DM; - buildDistanceMap(DM, I, MBB->end()); - // Find the register whose use is furthest away. - unsigned SReg = 0; - unsigned MaxDist = 0; - MachineInstr *MaxUseMI = 0; - int Reg = Candidates.find_first(); - while (Reg != -1) { - unsigned Dist; - MachineInstr *UseMI = findFirstUse(MBB, DM, Reg, Dist); - for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) { - unsigned AsDist; - MachineInstr *AsUseMI = findFirstUse(MBB, DM, *AS, AsDist); - if (AsDist < Dist) { - Dist = AsDist; - UseMI = AsUseMI; - } - } + MachineBasicBlock::iterator UseMI; + unsigned SReg = findSurvivorReg(I, Candidates, 25, UseMI); - // If we found an unused register there is no reason to spill it. We have - // probably found a callee-saved register that has been saved in the - // prologue, but happens to be unused at this point. - if (!isAliasUsed(Reg)) - return Reg; - - if (Dist >= MaxDist) { - MaxDist = Dist; - MaxUseMI = UseMI; - SReg = Reg; - } - Reg = Candidates.find_next(Reg); - } + // If we found an unused register there is no reason to spill it. We have + // probably found a callee-saved register that has been saved in the + // prologue, but happens to be unused at this point. + if (!isAliasUsed(SReg)) + return SReg; assert(ScavengedReg == 0 && "Scavenger slot is live, unable to scavenge another register!"); @@ -377,16 +334,24 @@ unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC, // Avoid infinite regress ScavengedReg = SReg; - // Spill the scavenged register before I. - TII->storeRegToStackSlot(*MBB, I, SReg, true, ScavengingFrameIndex, RC); - MachineBasicBlock::iterator II = prior(I); - TRI->eliminateFrameIndex(II, SPAdj, this); + // If the target knows how to save/restore the register, let it do so; + // otherwise, use the emergency stack spill slot. + if (!TRI->saveScavengerRegister(*MBB, I, UseMI, RC, SReg)) { + // Spill the scavenged register before I. + assert(ScavengingFrameIndex >= 0 && + "Cannot scavenge register without an emergency spill slot!"); + TII->storeRegToStackSlot(*MBB, I, SReg, true, ScavengingFrameIndex, RC); + MachineBasicBlock::iterator II = prior(I); + TRI->eliminateFrameIndex(II, SPAdj, NULL, this); + + // Restore the scavenged register before its use (or first terminator). + TII->loadRegFromStackSlot(*MBB, UseMI, SReg, ScavengingFrameIndex, RC); + II = prior(UseMI); + TRI->eliminateFrameIndex(II, SPAdj, NULL, this); + } + + ScavengeRestore = prior(UseMI); - // Restore the scavenged register before its use (or first terminator). - II = MaxUseMI - ? MachineBasicBlock::iterator(MaxUseMI) : MBB->getFirstTerminator(); - TII->loadRegFromStackSlot(*MBB, II, SReg, ScavengingFrameIndex, RC); - ScavengeRestore = prior(II); // Doing this here leads to infinite regress. // ScavengedReg = SReg; ScavengedRC = RC;